High strength foil journal bearing retainer

ABSTRACT

A journal foil bearing includes a bearing retainer having one slot configured to receive a top foil leading edge tab and another slot configured to receive a top foil trailing edge tab. A backup support structure, integral to the bearing retainer, extends between and is at least partially defined by the slots. The retainer is configured so that, during operation, the trailing edge tab further contacts, at an increased contact pressure, the support structure at a position close to the friction force, thereby minimizing top foil bending stress and improving bearing strength.

BACKGROUND OF THE INVENTION

The present invention generally relates to foil journal bearings and,more particularly, to foil journal bearing retainers.

A foil journal bearing may be a fluid film hydrodynamic bearing and maybe used to support a high speed rotating member, such as a shaft. Thefoil journal bearing, which may be configured to enclose the rotatingmember, may include a close-fitting, compliant, annular element such asa thin foil encased within a stationary retaining member. Rotation ofthe shaft within the retaining member may form and maintain apressurized fluid film between the shaft and the compliant foil. Highspeed rotation of the shaft may generate a high pressure in the fluidfilm and this pressurized fluid film may support the load imposed by theshaft.

The compliant foil, such as a top foil, may be secured to the retainingmember by edge tabs, also referred to as retaining tabs. The word“compliant” may be defined as “yielding” and a compliant foil may be afoil that is configured to yield, for example, to the pressurized fluidfilm. A resilient backing member, such as a spring foil, may be disposedbetween the top foil and the retaining member to accommodate deflectionsof the foil resulting from pressurization, centrifugal forces andtemperature differentials in order to maintain adequate film layergeometry. For some applications, a second compliant foil, such as anunder foil, may be disposed between the top foil and the spring foil.

During operation, foil journal bearings can experience highcircumferential forces when the fluid film is compromised in an overloadcondition. These forces are transmitted to the top foil retaining taband produce a high bending moment and subsequent stress in the top foilthat can permanently distort the tab, affect bearing performance andshorten bearing life.

As can be seen, a higher strength retaining design is needed that willprevent loss in bearing performance and shortened bearing life. Thedesign must be simple to minimize manufacturing cost.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an apparatus forming a foiljournal bearing comprises a retainer member having an inner surface thatdefines an opening, said opening configured to receive a rotatablemember; a top foil trailing edge tab slot extending into said retainermember; a top foil leading edge tab slot extending into said retainermember; a top foil having a trailing edge tab and a leading edge tab;wherein the trailing edge tab is disposed in the trailing edge tab slot;wherein the leading edge tab is disposed in the leading edge tab slot; abackup support structure positioned between and at least partiallydefined by said top foil trailing edge tab slot and said top foilleading edge tab slot, and said backup support structure integral tosaid retainer member; whereupon, in the absence of rotation of therotatable member, the trailing edge tab is in contact, at an initialcontact pressure, with the backup support; whereupon, during rotation ofthe rotatable member, the trailing edge tab is urged into increasedcontact, at a subsequent contact pressure higher than the initialcontact pressure, with the backup support.

In another aspect of the present invention, an apparatus comprises a topfoil having a first segment and a second segment; wherein the firstsegment includes a top foil trailing edge tab; wherein the trailing edgetab includes a trailing edge tab distal end and a trailing edge tabopposite end; wherein the second segment includes a top foil leadingedge tab; a retaining system coupled with said top foil and configuredto at least partially enclose a rotatable member, said retaining systemhaving a backup support structure, a trailing edge tab slot, and aleading edge tab slot; wherein the trailing edge tab is disposed in thetrailing edge tab slot; wherein the leading edge tab is disposed in theleading edge tab slot; whereupon a friction force to the first segmenturges only the trailing edge tab opposite end into increased contact, atan increased contact pressure, with the backup support structure.

In a further aspect of the present invention, a method of supporting arotatable member comprises the steps of installing a compliant assemblyin a retaining system to form a journal foil bearing, said retainingsystem including a retainer member; installing a top foil within saidjournal foil bearing, the top foil having a portion positioned adjacentthe rotatable member; wherein the portion includes a tab having a distalend and an opposite end; installing the rotatable member in saidretainer member within said journal foil bearing; and rotating saidrotatable member to form a pressurized fluid film between said rotatablemember and said compliant assembly such that only the opposite end ofthe tab of the top foil that is positioned adjacent the rotatable memberis urged into increased contact, at an increased contact pressure, withthe retainer member to minimize bending moment and stress in the topfoil during rotation of the rotatable member

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdrawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a portion of a foil journal bearingaccording to one embodiment of the present invention;

FIG. 2 is a cross sectional view of a portion of a foil journal bearingaccording to another embodiment of the present invention; and

FIG. 3 is a flow chart of a method of supporting a rotatable memberaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplatedmodes of carrying out exemplary embodiments of the invention. Thedescription is not to be taken in a limiting sense, but is made merelyfor the purpose of illustrating the general principles of the invention,since the scope of the invention is best defined by the appended claims.

Various inventive features are described below that can each be usedindependently of one another or in combination with other features.

Broadly, embodiments of the present invention provide high strength foiljournal bearing retainers. Embodiments of the present invention may findbeneficial use in industries such as aerospace. Embodiments of thepresent invention may be useful in applications including auxiliarypower units (APU) and air cycle machines (ACM). Embodiments of thepresent invention may be useful in any foil bearing applicationincluding, but not limited to, cryogenic turbo-rotors, turbochargers,air conditioning machines, gas turbine engines, motor drivencompressors, fans, blowers, turboalternators, and turbogenerators.

A journal foil bearing 130, according to an embodiment of the presentinvention, is shown in FIG. 1. The journal foil bearing 230, accordingto another embodiment of the present invention, is shown in FIG. 2.Referring to FIGS. 1 and 2, the journal foil bearing 130, 230 may beconfigured to support a rotatable member 132, 232 such as a shaft. Thejournal foil bearing 130, 230 may include a retaining system 134, 234and a compliant assembly 136, 236.

The retaining system 134, 234 may include a retainer member 138, 238, anopening 140, 240, a top foil trailing edge tab slot 142, 242, a top foilleading edge tab slot 144, 244 and a backup support structure 146, 246.The terms “leading” and “trailing” may be defined with reference to thedirection of rotation of the rotatable member 132, 232. For example, inFIGS. 1 and 2, if the rotatable member 132, 232 rotates counterclockwisethe trailing edge tab slot 142, 242 may have a portion to extend towardsthe right side of the figure and the top foil leading edge tab slot 144,244 may have a portion to extend towards the left side of the figure.The compliant assembly 136, 236 may include a top foil 148, 248 having atop foil trailing edge tab 150, 250 and a top foil leading edge tab 152,252. The compliant assembly 136, 236 also may include a spring foil (notshown) disposed between the top foil 148, 248 and the retainer member138, 238 to accommodate deflections of the top foil 148, 248. For someembodiments, the compliant assembly 136, 236 also may include an underfoil (not shown) disposed between the top foil 148, 248 and the springfoil for additional support.

The retainer member 138, 238 may comprise a base structure having aninner surface 156, 256 that may define the opening 140, 240. For someembodiments, the retainer member 138, 238 may comprise metal. Theopening 140, 240 may extend through the retainer member 138, 238 and maybe configured to receive and to at least partially enclose the rotatablemember 132, 232. For some embodiments, the opening 140, 240 may becylindrical.

The top foil trailing edge tab slot 142, 242 may comprise a slotextending outward from the opening 140, 240 and into the retainer member138, 238. For some embodiments, the top foil trailing edge tab slot 142,242 may be formed by electrical discharge machining (EDM), extrusion,casting, or broaching.

The top foil trailing edge tab slot 142, 242 may be configured toreceive the top foil trailing edge tab 150, 250. The dimensions of thetop foil trailing edge tab slot 142, 242 may vary and may depend on thedimensions of the top foil trailing edge tab 150, 250 and on theapplication. For some embodiments, the top foil trailing edge tab slot142, 242 may have a trailing slot depth 160, 260, as measured outwardfrom the opening 140, 240 and through the trailing edge tab slot 142,242, of between about 0.02 inch and about 0.5 inch. For some embodimentswherein the opening 140, 240 is cylindrical, the trailing slot depth160, 260 may be less than about 25% of the diameter of the opening 140,240. For some embodiments, the top foil trailing edge tab slot 142, 242may have a trailing slot width 162, 262, as measured perpendicular tothe trailing slot depth 160, 260, of between about 0.005 inch and about0.5 inch.

The retaining system 134, 234 may include at least one top foil trailingedge tab slot 142, 242. For some embodiments, the retaining system 134,234 may include a plurality of top foil trailing edge tab slots 142,242. For example, when the top foil 148, 248 is a segmented top foilcomprising three foil segments, each foil segment subtending acircumferential segment of the inner surface 156, 256 and including atop foil trailing edge tab 150, 250, the retaining system 134, 234 mayinclude three top foil trailing edge tab slots 142, 242.

The top foil 148, 248 may include no segments or any number of foilsegments, and the retaining system 134, 234 may include any number oftop foil trailing edge tab slots 142, 242. The top foil 148, 248 may bean un-segmented top foil or a segmented top foil and may comprise aplurality of foil segments, each foil segment subtending acircumferential segment of the inner surface 156, 256 and including atop foil trailing edge tab 150, 250.

The top foil leading edge tab slot 144, 244 may include a slot extendingoutward from the opening 140, 240 and into the retainer member 138, 238.For some embodiments, the top foil leading edge tab slot 144, 244 may beformed by EDM or by extrusion casting, or broaching processes.

The top foil leading edge tab slot 144, 244 may be configured to receivethe top foil leading edge tab 152, 252. The dimensions of the top foilleading edge tab slot 144, 244 may vary and may depend on the dimensionsof the top foil leading edge tab 152, 252 and on the application. Forsome embodiments, the top foil leading edge tab slot 144, 244 may have aleading slot depth 164, 264, as measured outward from the opening 140,240 and through the leading edge tab slot 144, 244, of between about0.02 inch and about 0.5 inch. For some embodiments, the leading slotdepth 164, 264 may be less than about 25% of the diameter of the opening140, 240. For some embodiments, the top foil leading edge tab slot 144,244 may have a leading slot width 166, 266, as measured perpendicular tothe leading slot depth 164, 264, of between about 0.005 inch and about0.5 inch.

The retaining system 134, 234 may include at least one top foil leadingedge tab slot 144, 244. For some embodiments, the retaining system 134,234 may include a plurality of top foil leading edge tab slots 144, 244.For example, when the top foil 148, 248 is a segmented top foilcomprising three foil segments, each foil segment subtending acircumferential segment of the inner surface 156, 256 and including atop foil leading edge tab 152, 252, the retaining system 134, 234 mayinclude three top foil leading edge tab slots 144, 244.

The top foil 148, 248 may include any number of foil segments and theretaining system 134, 234 may include any number of top foil leadingedge tab slots 144, 244. The top foil 148, 248 may be a segmented topfoil and may comprise a plurality of foil segments, each foil segmentsubtending a circumferential segment of the inner surface 156, 256 andincluding a top foil leading edge tab 152, 252.

For mistake proof installation, the leading slot depth 164, 264 may begreater than or less than the trailing slot depth 160, 260, as betterseen in FIG. 2. In other words, the leading edge tab slot 144, 244 andthe trailing edge tab slot 142, 242 may have depths of unequalmagnitude. For some applications, the top foil leading edge tab slot 144may be canted, as shown in FIG. 1, to reduce installation errors.

For some embodiments, the leading slot width 166, 266 may be greaterthan the trailing slot width 162, 262 to prevent or reduce contactbetween the top foil leading edge tab 152, 252 and the retainer member138, 238. For some applications, the leading slot width 166, 266 may beless than, or equal to, the trailing slot width 162, 262.

For some embodiments, a distance 180, 280 between the leading edge tabslot 144, 244 and the trailing edge tab slot 142, 242, as measured alongthe inner surface 156, 256, may be less than about 0.5 inch. For someembodiments, the distance 180, 280 between the leading edge tab slot144, 244 and the trailing edge tab slot 142, 242 may be between about0.005 inch and about 0.5 inch. For some embodiments, the distance 180,280 between the leading edge tab slot 144, 244 and the trailing edge tabslot 142, 242 may be less than about 0.005 inch.

The backup support structure 146, 246 may be integral to the retainermember 138, 238. The backup support structure 146, 246 may be at leastpartially defined by the top foil trailing edge tab slot 142, 242 andthe top foil leading edge tab slot 144, 244. The backup supportstructure 146, 246 may extend circumferentially between the top foiltrailing edge tab slot 142, 242 and the top foil leading edge tab slot144, 244.

During operation, the backup support structure 146, 246 may increasebearing strength by reducing bending stress of the top foil 148, 248.Rotation of the rotatable member 132, 232 may produce a friction force170, 270 that may urge the top foil 148, 248 circumferentially in thedirection of rotation.

During operation, the top foil trailing edge tab 150, 252 may be urgedtoward the backup support structure 146, 246. In some embodiments, aportion 172, 272 of the top foil trailing edge tab 150, 252 that ispositioned adjacent the rotatable member 132, 232 may be out of contactwith the backup support structure 146, 246, in the absence of rotationof the rotatable member. The support structure 146, 246 may then beurged into contact, with the backup support structure 146, 246, when therotatable member is rotating, as shown in FIGS. 1 and 2. In otherembodiments, the portion 172, 272 may be in contact, at an initialcontact pressure, with the backup support structure 146, 246, when therotatable member is not rotating. When the rotatable member is rotating,the portion 172, 272 may then be urged into increased or greatercontact, at a subsequent contact pressure higher than the initialcontact pressure, with the backup support structure 146, 246.

Contact between the backup support structure 146, 246 and the portion172, 272 of the top foil trailing edge tab 150, 250 that is positionedadjacent the rotatable member 132, 232 may provide a reaction force 174,274 at a position close to the friction force 170, 270. The top foiltrailing edge tab 150, 250 may be configured to be urged toward thebackup support structure 146, 246 such that the portion 172, 272 that ispositioned adjacent the rotatable member 132, 232 is urged into initialor increased contact with the backup support structure 146, 246 duringoperation (e.g. rotation of the rotatable member 132, 232), therebyminimizing bending moment and metal stress in the top foil 148, 248.

The compliant assembly 136, 236, which may comprise thin sheet metal,may be disposed radially outward from the rotatable member 132, 232 andmay be configured to be in operational communication with a pressurizedfluid film (not shown). For some embodiments, the fluid film maycomprise air. The fluid film may comprise any viscous fluid. Forexample, the fluid film may comprise fluids, such as but not limited to,liquid or gaseous hydrogen, oxygen, and refrigerants.

The compliant assembly 136, 236 may be coupled to the retainer member138, 238. The top foil trailing edge tab 150, 250 may be configured tobe installed in the top foil trailing edge tab slot 142, 242. The topfoil leading edge tab 152, 252 may be configured to be installed in thetop foil leading edge tab slot 144, 244.

For some embodiments including the spring foil, the leading edge and/orthe trailing edge of the spring foil 154, 254 may be coupled to theretainer member 138, 238. For some embodiments including the under foil,the leading edge and/or the trailing edge of the spring foil 154, 254may be coupled to the retainer member 138, 238.

Referring to FIG. 3, a method 300 of supporting a rotatable member 132,232 according to one embodiment of the present invention is shown. Themethod 300 may include a step 310 of installing a compliant assembly136, 236 in a retaining system 134, 234 to form a journal foil bearing130, 230, the retaining system 134, 234 including a retainer member 138,238; a step 320 of installing a top foil 148, 248 within the journalfoil bearing 130, 230, the top foil 148, 248 having a portion 172, 272positioned adjacent the rotatable member 132, 232; a step 330 ofinstalling the rotatable member 132, 232 in the journal foil bearing130, 230; and a step 340 of rotating the rotatable member 132, 232 toform a pressurized fluid film between the rotatable member 132, 232 andthe compliant assembly 136, 236 such that the portion 172, 272 of topfoil 148, 248 that is positioned adjacent the rotatable member 132, 232is urged into initial or increased/greater contact with the retainermember 138, 238 to minimize bending moment and stress in the top foil148, 248 during rotation of the rotatable member 132, 232 with orwithout the pressurized fluid film.

The step 310 of installing the compliant assembly 136, 236 in theretaining system 134 234 to form the journal foil bearing 130, 230 maycomprise positioning a top foil trailing edge tab 150, 250 of thecompliant assembly 136, 236 in a top foil trailing edge tab slot 142,242 of the retaining system 134, 234 and positioning a top foil leadingedge tab 152, 252 of the compliant assembly 136, 236 in a top foilleading edge tab slot 144, 244 of the retaining system 134, 234 suchthat a backup support structure 146, 246 of the retaining system 134,234 is positioned between the top foil trailing edge tab 150, 250 andthe top foil leading edge tab 152, 252.

The step 330 of installing the rotatable member 132, 232 in the retainermember 138, 238 within the journal foil bearing 130, 230 may comprisepositioning the rotatable member 132, 232 radially inward from thecompliant assembly 136, 236. For some applications, the step 330 ofinstalling the rotatable member 132, 232 in the journal foil bearing130, 230 may comprise positioning a shaft of an auxiliary power unit inthe journal foil bearing 130, 230. For some applications, the step 330of installing the rotatable member 132, 232 in the journal foil bearing130, 230 may comprise positioning a shaft of an air cycle machine in thejournal foil bearing 130, 230. For some applications, the step 330 ofinstalling the rotatable member 132, 232 in the journal foil bearing130, 230 may comprise positioning a shaft of an auxiliary power unit, anair cycle machine, a turbocompressor, a motor driven compressor, a fan,a blower, a turbogenerator, or a turboalternator in the journal foilbearing 130, 230.

The step 340 of rotating the rotatable member 132, 232 to form apressurized fluid film between the rotatable member 132, 232 and thecompliant assembly 136, 236 may comprise rotating the rotatable member132, 232. The step 340 of rotating the rotatable member 132, 232 to forma pressurized fluid film between the rotatable member 132, 232 and thecompliant assembly 136, 236 may include contacting the rotatable member132, 232 under overload condition resulting in the compliant assembly136, 236, initially or further contacting the trailing edge tab 150, 250to the backup support structure 146, 246 at a position close to thefriction force produced during operation, thereby minimizing top foilbending stress and improving bearing strength.

As can be appreciated by those skilled in the art, embodiments of thepresent invention can reduce the bending moment and metal stress in thetop foil 148, 248 by incorporating the backup support structure 146, 246close to the circumferential force vector.

It should be understood, of course, that the foregoing relates toexemplary embodiments of the invention and that modifications may bemade without departing from the spirit and scope of the invention as setforth in the following claims.

We claim:
 1. An apparatus forming a foil journal bearing comprising: aretainer member having an inner surface that defines an opening, saidopening configured to receive a rotatable member; a top foil trailingedge tab slot extending into said retainer member; a top foil leadingedge tab slot extending into said retainer member; a top foil having atrailing edge tab and a leading edge tab; wherein said top foil leadingedge tab slot has a leading slot width, said top foil trailing edge tabslot has a trailing slot width, and said leading slot width is one ofgreater than, less than, and equal to said trailing slot width; whereinthe trailing edge tab is disposed in the trailing edge tab slot; whereinthe leading edge tab is disposed in the leading edge tab slot; a backupsupport structure positioned between and at least partially defined bysaid top foil trailing edge tab slot and said top foil leading edge tabslot, and said backup support structure integral to said retainermember; whereupon, in the absence of rotation of the rotatable member,the trailing edge tab is in contact, at an initial contact pressure,with the backup support; whereupon, during rotation of the rotatablemember, the trailing edge tab is urged into increased contact, at asubsequent contact pressure higher than the initial contact pressure,with the backup support.
 2. The apparatus of claim 1, wherein said topfoil leading edge tab slot is canted.
 3. The apparatus of claim 1,wherein a distance between said leading edge tab slot and said trailingedge tab slot is less than about 0.5 inches.
 4. The apparatus of claim1, wherein said retainer member forms the opening in a cylindrical shapeand said top foil trailing edge tab slot has a trailing slot depth ofless than about 25% of the diameter of said opening.
 5. The apparatus ofclaim 1, wherein said backup support structure extends circumferentiallybetween said top foil trailing edge tab slot and said top foil leadingedge tab slot.